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Chau DDL, Li W, Chan WWR, Sun JKL, Zhai Y, Chow HM, Lau KF. Insulin stimulates atypical protein kinase C-mediated phosphorylation of the neuronal adaptor FE65 to potentiate neurite outgrowth by activating ARF6-Rac1 signaling. FASEB J 2022; 36:e22594. [PMID: 36250347 DOI: 10.1096/fj.202200757r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 08/21/2022] [Accepted: 09/26/2022] [Indexed: 11/11/2022]
Abstract
Neurite outgrowth is a fundamental process in neurons that produces extensions and, consequently, neural connectivity. Neurite damage and atrophy are observed in various brain injuries and disorders. Understanding the intrinsic pathways of neurite outgrowth is essential for developing strategies to stimulate neurite regeneration. Insulin is a pivotal hormone in the regulation of glucose homeostasis. There is increasing evidence for the neurotrophic functions of insulin, including the induction of neurite outgrowth. However, the associated mechanism remains elusive. Here, we demonstrate that insulin potentiates neurite outgrowth mediated by the small GTPases ADP-ribosylation factor 6 (ARF6) and Ras-related C3 botulinum toxin substrate 1 (Rac1) through the neuronal adaptor FE65. Moreover, insulin enhances atypical protein kinase Cι/λ (PKCι/λ) activation and FE65 phosphorylation at serine 459 (S459) in neurons and mouse brains. In vitro and cellular assays show that PKCι/λ phosphorylated FE65 at S459. Consistently, insulin potentiates FE65 S459 phosphorylation only in the presence of PKCι/λ. Phosphomimetic studies show that an FE65 S459E mutant potently activates ARF6, Rac1, and neurite outgrowth. Notably, this phosphomimetic mutation enhances the FE65-ARF6 interaction, a process that promotes ARF6-Rac1-mediated neurite outgrowth. Likewise, insulin treatment and PKCι/λ overexpression potentiate the FE65-ARF6 interaction. Conversely, PKCι/λ knockdown suppresses the stimulatory effect of FE65 on ARF6-Rac1-mediated neurite outgrowth. The effect of insulin on neurite outgrowth is also markedly attenuated in PKCι/λ knockdown neurons, in the presence and absence of FE65. Our findings reveal a novel mechanism linking insulin with ARF6-Rac1-dependent neurite extension through the PKCι/λ-mediated phosphorylation of FE65.
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Affiliation(s)
- Dennis Dik-Long Chau
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Wen Li
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China.,Research Laboratory for Biomedical Optics and Molecular Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Wai Wa Ray Chan
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Jacquelyne Ka-Li Sun
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Yuqi Zhai
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Hei-Man Chow
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Kwok-Fai Lau
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
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Argaev-Frenkel L, Rosenzweig T. Complexity of NAC Action as an Antidiabetic Agent: Opposing Effects of Oxidative and Reductive Stress on Insulin Secretion and Insulin Signaling. Int J Mol Sci 2022; 23:ijms23062965. [PMID: 35328386 PMCID: PMC8950759 DOI: 10.3390/ijms23062965] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 03/01/2022] [Accepted: 03/07/2022] [Indexed: 02/05/2023] Open
Abstract
Dysregulated redox balance is involved in the pathogenesis of type 2 diabetes. While the benefit of antioxidants in neutralizing oxidative stress is well characterized, the potential harm of antioxidant-induced reductive stress is unclear. The aim of this study was to investigate the dose-dependent effects of the antioxidant N-acetylcysteine (NAC) on various tissues involved in the regulation of blood glucose and the mechanisms underlying its functions. H2O2 was used as an oxidizing agent in order to compare the outcomes of oxidative and reductive stress on cellular function. Cellular death in pancreatic islets and diminished insulin secretion were facilitated by H2O2-induced oxidative stress but not by NAC. On the other hand, myotubes and adipocytes were negatively affected by NAC-induced reductive stress, as demonstrated by the impaired transmission of insulin signaling and glucose transport, as opposed to H2O2-stimulatory action. This was accompanied by redox balance alteration and thiol modifications of proteins. The NAC-induced deterioration of insulin signaling was also observed in healthy mice, while both insulin secretion and insulin signaling were improved in diabetic mice. This study establishes the tissue-specific effects of NAC and the importance of the delicate maintenance of redox balance, emphasizing the challenge of implementing antioxidant therapy in the clinic.
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Affiliation(s)
| | - Tovit Rosenzweig
- Department of Molecular Biology, Ariel University, Ariel 4070000, Israel;
- Department of Nutritional Studies, Ariel University, Ariel 4070000, Israel
- Correspondence: ; Tel.: +972-3937-1433
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Gallenga CE, Lonardi M, Pacetti S, Violanti SS, Tassinari P, Di Virgilio F, Tognon M, Perri P. Molecular Mechanisms Related to Oxidative Stress in Retinitis Pigmentosa. Antioxidants (Basel) 2021; 10:antiox10060848. [PMID: 34073310 PMCID: PMC8229325 DOI: 10.3390/antiox10060848] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 05/13/2021] [Accepted: 05/20/2021] [Indexed: 12/17/2022] Open
Abstract
Retinitis pigmentosa (RP) is an inherited retinopathy. Nevertheless, non-genetic biological factors play a central role in its pathogenesis and progression, including inflammation, autophagy and oxidative stress. The retina is particularly affected by oxidative stress due to its high metabolic rate and oxygen consumption as well as photosensitizer molecules inside the photoreceptors being constantly subjected to light/oxidative stress, which induces accumulation of ROS in RPE, caused by damaged photoreceptor’s daily recycling. Oxidative DNA damage is a key regulator of microglial activation and photoreceptor degeneration in RP, as well as mutations in endogenous antioxidant pathways involved in DNA repair, oxidative stress protection and activation of antioxidant enzymes (MUTYH, CERKL and GLO1 genes, respectively). Moreover, exposure to oxidative stress alters the expression of micro-RNA (miRNAs) and of long non-codingRNA (lncRNAs), which might be implicated in RP etiopathogenesis and progression, modifying gene expression and cellular response to oxidative stress. The upregulation of the P2X7 receptor (P2X7R) also seems to be involved, causing pro-inflammatory cytokines and ROS release by macrophages and microglia, contributing to neuroinflammatory and neurodegenerative progression in RP. The multiple pathways analysed demonstrate that oxidative microglial activation may trigger the vicious cycle of non-resolved neuroinflammation and degeneration, suggesting that microglia may be a key therapy target of oxidative stress in RP.
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Affiliation(s)
- Carla Enrica Gallenga
- Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy; (C.E.G.); (F.D.V.); (M.T.)
| | - Maria Lonardi
- Department of Specialized Surgery, Section of Ophthalmology, Sant’Anna University Hospital, 44121 Ferrara, Italy; (M.L.); (S.P.); (P.T.)
| | - Sofia Pacetti
- Department of Specialized Surgery, Section of Ophthalmology, Sant’Anna University Hospital, 44121 Ferrara, Italy; (M.L.); (S.P.); (P.T.)
| | - Sara Silvia Violanti
- Department of Head and Neck, Section of Ophthalmology, San Paolo Hospital, 17100 Savona, Italy;
| | - Paolo Tassinari
- Department of Specialized Surgery, Section of Ophthalmology, Sant’Anna University Hospital, 44121 Ferrara, Italy; (M.L.); (S.P.); (P.T.)
| | - Francesco Di Virgilio
- Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy; (C.E.G.); (F.D.V.); (M.T.)
| | - Mauro Tognon
- Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy; (C.E.G.); (F.D.V.); (M.T.)
| | - Paolo Perri
- Department of Neuroscience and Rehabilitation, Section of Ophthalmology, University of Ferrara, 44121 Ferrara, Italy
- Correspondence:
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Donato L, Scimone C, Alibrandi S, Rinaldi C, Sidoti A, D’Angelo R. Transcriptome Analyses of lncRNAs in A2E-Stressed Retinal Epithelial Cells Unveil Advanced Links between Metabolic Impairments Related to Oxidative Stress and Retinitis Pigmentosa. Antioxidants (Basel) 2020; 9:E318. [PMID: 32326576 PMCID: PMC7222347 DOI: 10.3390/antiox9040318] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2020] [Revised: 04/08/2020] [Accepted: 04/14/2020] [Indexed: 12/12/2022] Open
Abstract
: Long non-coding RNAs (lncRNAs) are untranslated transcripts which regulate many biological processes. Changes in lncRNA expression pattern are well-known related to various human disorders, such as ocular diseases. Among them, retinitis pigmentosa, one of the most heterogeneous inherited disorder, is strictly related to oxidative stress. However, little is known about regulative aspects able to link oxidative stress to etiopathogenesis of retinitis. Thus, we realized a total RNA-Seq experiment, analyzing human retinal pigment epithelium cells treated by the oxidant agent N-retinylidene-N-retinylethanolamine (A2E), considering three independent experimental groups (untreated control cells, cells treated for 3 h and cells treated for 6 h). Differentially expressed lncRNAs were filtered out, explored with specific tools and databases, and finally subjected to pathway analysis. We detected 3,3'-overlapping ncRNAs, 107 antisense, 24 sense-intronic, four sense-overlapping and 227 lincRNAs very differentially expressed throughout all considered time points. Analyzed lncRNAs could be involved in several biochemical pathways related to compromised response to oxidative stress, carbohydrate and lipid metabolism impairment, melanin biosynthetic process alteration, deficiency in cellular response to amino acid starvation, unbalanced regulation of cofactor metabolic process, all leading to retinal cell death. The explored lncRNAs could play a relevant role in retinitis pigmentosa etiopathogenesis, and seem to be the ideal candidate for novel molecular markers and therapeutic strategies.
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Affiliation(s)
- Luigi Donato
- Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Division of Medical Biotechnologies and Preventive Medicine, University of Messina, 98125 Messina, Italy
- Department of Biomolecular Strategies, Genetics and Avant-Garde Therapies, I.E.ME.S.T., 90139 Palermo, Italy
| | - Concetta Scimone
- Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Division of Medical Biotechnologies and Preventive Medicine, University of Messina, 98125 Messina, Italy
- Department of Biomolecular Strategies, Genetics and Avant-Garde Therapies, I.E.ME.S.T., 90139 Palermo, Italy
| | - Simona Alibrandi
- Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Division of Medical Biotechnologies and Preventive Medicine, University of Messina, 98125 Messina, Italy
- Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina, 98125 Messina, Italy
| | - Carmela Rinaldi
- Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Division of Medical Biotechnologies and Preventive Medicine, University of Messina, 98125 Messina, Italy
| | - Antonina Sidoti
- Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Division of Medical Biotechnologies and Preventive Medicine, University of Messina, 98125 Messina, Italy
- Department of Biomolecular Strategies, Genetics and Avant-Garde Therapies, I.E.ME.S.T., 90139 Palermo, Italy
| | - Rosalia D’Angelo
- Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Division of Medical Biotechnologies and Preventive Medicine, University of Messina, 98125 Messina, Italy
- Department of Biomolecular Strategies, Genetics and Avant-Garde Therapies, I.E.ME.S.T., 90139 Palermo, Italy
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The Small GTPase Arf6: An Overview of Its Mechanisms of Action and of Its Role in Host⁻Pathogen Interactions and Innate Immunity. Int J Mol Sci 2019; 20:ijms20092209. [PMID: 31060328 PMCID: PMC6539230 DOI: 10.3390/ijms20092209] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 04/26/2019] [Accepted: 04/27/2019] [Indexed: 12/15/2022] Open
Abstract
The small GTase Arf6 has several important functions in intracellular vesicular trafficking and regulates the recycling of different types of cargo internalized via clathrin-dependent or -independent endocytosis. It activates the lipid modifying enzymes PIP 5-kinase and phospholipase D, promotes actin polymerization, and affects several functionally distinct processes in the cell. Arf6 is used for the phagocytosis of pathogens and can be directly or indirectly targeted by various pathogens to block phagocytosis or induce the uptake of intracellular pathogens. Arf6 is also used in the signaling of Toll-like receptors and in the activation of NADPH oxidases. In this review, we first give an overview of the different roles and mechanisms of action of Arf6 and then focus on its role in innate immunity and host–pathogen interactions.
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Zhao J, Wang M, Deng W, Zhong D, Jiang Y, Liao Y, Chen B, Zhang X. ADP-ribosylation factor-like GTPase 15 enhances insulin-induced AKT phosphorylation in the IR/IRS1/AKT pathway by interacting with ASAP2 and regulating PDPK1 activity. Biochem Biophys Res Commun 2017; 486:865-871. [PMID: 28322786 DOI: 10.1016/j.bbrc.2017.03.079] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Accepted: 03/16/2017] [Indexed: 10/19/2022]
Abstract
Decreased phosphorylation in the insulin signalling pathway is a hallmark of insulin resistance. The causes of this phenomenon are complicated and multifactorial. Recently, genomic analyses have identified ARL15 as a new candidate gene related to diabetes. However, the ARL15 protein function remains unclear. Here, we show that ARL15 is upregulated by insulin stimulation. This effect was impaired in insulin-resistant pathophysiology in TNF-α-treated C2C12 myotubes and in the skeletal muscles of leptin knockout mice. In addition, ARL15 localized to the cytoplasm in the resting state and accumulated in the Golgi apparatus around the nucleus upon insulin stimulation. ARL15 overexpression can enhance the phosphorylation of the key insulin signalling pathway molecules IR, IRS1 and AKT in C2C12 myotubes. Moreover, ARL15 knockdown can also specifically inhibit the phosphorylation of PDPK1 Ser241, thereby reducing PDPK1 activity and its downstream phosphorylation of AKT Thr308. Co-immunoprecipitation assays identified ASAP2 as an ARL15-interacting protein. In conclusion, we have identified that ARL15 acts as an insulin-sensitizing effector molecule to upregulate the phosphorylation of members of the canonical IR/IRS1/PDPK1/AKT insulin pathway by interacting with its GAP ASAP2 and activating PDPK1. This research may provide new insights into GTPase-mediated insulin signalling regulation and facilitate the development of new pharmacotherapeutic targets for insulin sensitization.
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Affiliation(s)
- Jie Zhao
- Department of Endocrinology, Southwest Hospital, Third Military Medical University, Chongqing 400038, China
| | - Min Wang
- Department of Endocrinology, Southwest Hospital, Third Military Medical University, Chongqing 400038, China
| | - Wuquan Deng
- Department of Endocrinology and Nephrology, Emergency Medical Center, Chongqing 400014, China
| | - Daping Zhong
- Department of Endocrinology, 324th Hospital of the People's Liberation Army (No. 324 Hospital of PLA), Chongqing 400020, China
| | - Youzhao Jiang
- Department of Endocrinology, Southwest Hospital, Third Military Medical University, Chongqing 400038, China
| | - Yong Liao
- Department of Endocrinology, 169th Hospital of the People's Liberation Army (No. 169 Hospital of PLA), Hengyang, Hunan Province, 421002, China
| | - Bing Chen
- Department of Endocrinology, Southwest Hospital, Third Military Medical University, Chongqing 400038, China.
| | - Xiaoli Zhang
- Department of Clinical Laboratory, Southwest Hospital, Third Military Medical University, Chongqing 400038, China.
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7
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Pawar A, Meier JA, Dasgupta A, Diwanji N, Deshpande N, Saxena K, Buwa N, Inchanalkar S, Schwartz MA, Balasubramanian N. Ral-Arf6 crosstalk regulates Ral dependent exocyst trafficking and anchorage independent growth signalling. Cell Signal 2016; 28:1225-1236. [PMID: 27269287 PMCID: PMC4973806 DOI: 10.1016/j.cellsig.2016.05.023] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Revised: 05/30/2016] [Accepted: 05/31/2016] [Indexed: 12/01/2022]
Abstract
Integrin dependent regulation of growth factor signalling confers anchorage dependence that is deregulated in cancers. Downstream of integrins and oncogenic Ras the small GTPase Ral is a vital mediator of adhesion dependent trafficking and signalling. This study identifies a novel regulatory crosstalk between Ral and Arf6 that controls Ral function in cells. In re-adherent mouse fibroblasts (MEFs) integrin dependent activation of RalA drives Arf6 activation. Independent of adhesion constitutively active RalA and RalB could both however activate Arf6. This is further conserved in oncogenic H-Ras containing bladder cancer T24 cells, which express anchorage independent active Ral that supports Arf6 activation. Arf6 mediates active Ral-exocyst dependent delivery of raft microdomains to the plasma membrane that supports anchorage independent growth signalling. Accordingly in T24 cells the RalB-Arf6 crosstalk is seen to preferentially regulate anchorage independent Erk signalling. Active Ral we further find uses a Ral-RalBP1-ARNO-Arf6 pathway to mediate Arf6 activation. This study hence identifies Arf6, through this regulatory crosstalk, to be a key downstream mediator of Ral isoform function along adhesion dependent pathways in normal and cancer cells. Ral mediates Arf6 activation downstream of integrins and oncogenic Ras. Arf6 mediates Ral-exocyst dependent delivery of raft microdomains. Active Ral supports anchorage independent Arf6 activation in bladder cancer T24 cells. Ral-Arf6 crosstalk in T24 cells regulates anchorage independent Erk signalling. A Ral-RalBP1-ARNO-Arf6 pathway mediates the Ral-Arf6 crosstalk.
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Affiliation(s)
- Archana Pawar
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
| | - Jeremy A Meier
- Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, VA 22908, United States
| | - Anwesha Dasgupta
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
| | - Neha Diwanji
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
| | - Neha Deshpande
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
| | - Kritika Saxena
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
| | - Natasha Buwa
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
| | - Siddhi Inchanalkar
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
| | - Martin Alexander Schwartz
- Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, VA 22908, United States; Yale Cardiovascular Research Center, 300 George Street, 7th Floor, New Haven, CT 06511, United States
| | - Nagaraj Balasubramanian
- Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India.
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8
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Govers R. Molecular mechanisms of GLUT4 regulation in adipocytes. DIABETES & METABOLISM 2014; 40:400-10. [DOI: 10.1016/j.diabet.2014.01.005] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 01/24/2014] [Accepted: 01/26/2014] [Indexed: 01/28/2023]
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Abstract
GLUT4 is regulated by its intracellular localization. In the absence of insulin, GLUT4 is efficiently retained intracellularly within storage compartments in muscle and fat cells. Upon insulin stimulation (and contraction in muscle), GLUT4 translocates from these compartments to the cell surface where it transports glucose from the extracellular milieu into the cell. Its implication in insulin-regulated glucose uptake makes GLUT4 not only a key player in normal glucose homeostasis but also an important element in insulin resistance and type 2 diabetes. Nevertheless, how GLUT4 is retained intracellularly and how insulin acts on this retention mechanism is largely unclear. In this review, the current knowledge regarding the various molecular processes that govern GLUT4 physiology is discussed as well as the questions that remain.
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10
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Béglé A, Tryoen-Tóth P, de Barry J, Bader MF, Vitale N. ARF6 regulates the synthesis of fusogenic lipids for calcium-regulated exocytosis in neuroendocrine cells. J Biol Chem 2009; 284:4836-45. [PMID: 19124467 DOI: 10.1074/jbc.m806894200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
An important role for specific lipids in membrane fusion has recently emerged, but regulation of their biosynthesis remains poorly understood. Among fusogenic lipids, phosphatidic acid and phosphoinositol 4,5-bisphosphate (PIP(2)) have been proposed to act at various steps of neurotransmitter and hormone exocytosis. Using real time FRET (fluorescence resonance energy transfer) measurements, we show here that the GTPase ARF6, potentially involved in the synthesis of these lipids, is activated at the exocytotic sites in PC12 cells stimulated for secretion. Depletion of endogenous ARF6 by siRNA dramatically inhibited secretagogue-evoked exocytosis. ARF6-siRNA greatly reduced secretagogue-evoked phospholipase D (PLD) activation and phosphatidic acid formation at the plasma membrane and moderately reduced constitutive levels of PIP(2) present at the plasma membrane in resting cells. Expression of an ARF6 insensitive to short interference RNA (siRNA) fully rescued secretion in ARF6-depleted cells. However, a mutated ARF6 protein specifically impaired in its ability to stimulate PLD had no effect. Finally, we show that the ARF6-siRNA-mediated inhibition of exocytosis could be rescued by an exogenous addition of lysophosphatidylcholine, a lipid that favors negative curvature on the inner leaflet of the plasma membrane. Altogether these data indicate that ARF6 is a critical upstream signaling element in the activation of PLD necessary to produce the fusogenic lipids required for exocytosis.
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Affiliation(s)
- Aurélie Béglé
- Département Neurotransmission et Sécrétion Neuroendocrine, Institut des Neurosciences Cellulaires et Intégratives (UPR 3212), Centre National de la Recherche Scientifique et Université de Strasbourg, 5 rue Blaise Pascal, 67084 Strasbourg, France
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11
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Yip MF, Ramm G, Larance M, Hoehn KL, Wagner MC, Guilhaus M, James DE. CaMKII-mediated phosphorylation of the myosin motor Myo1c is required for insulin-stimulated GLUT4 translocation in adipocytes. Cell Metab 2008; 8:384-98. [PMID: 19046570 DOI: 10.1016/j.cmet.2008.09.011] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/20/2007] [Revised: 03/02/2008] [Accepted: 09/19/2008] [Indexed: 11/26/2022]
Abstract
The unconventional myosin Myo1c has been implicated in insulin-regulated GLUT4 translocation to the plasma membrane in adipocytes. We show that Myo1c undergoes insulin-dependent phosphorylation at S701. Phosphorylation was accompanied by enhanced 14-3-3 binding and reduced calmodulin binding. Recombinant CaMKII phosphorylated Myo1c in vitro and siRNA knockdown of CaMKIIdelta abolished insulin-dependent Myo1c phosphorylation in vivo. CaMKII activity was increased upon insulin treatment and the CaMKII inhibitors CN21 and KN-62 or the Ca(2+) chelator BAPTA-AM blocked insulin-dependent Myo1c phosphorylation and insulin-stimulated glucose transport in adipocytes. Myo1c ATPase activity was increased after CaMKII phosphorylation in vitro and after insulin stimulation of CHO/IR/IRS-1 cells. Expression of wild-type Myo1c, but not S701A or ATPase dead mutant K111A, rescued the inhibition of GLUT4 translocation by siRNA-mediated Myo1c knockdown. These data suggest that insulin regulates Myo1c function via CaMKII-dependent phosphorylation, and these events play a role in insulin-regulated GLUT4 trafficking in adipocytes likely involving Myo1c motor activity.
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Affiliation(s)
- Ming Fai Yip
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW 2010, Australia
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12
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Adachi J, Kumar C, Zhang Y, Mann M. In-depth analysis of the adipocyte proteome by mass spectrometry and bioinformatics. Mol Cell Proteomics 2007; 6:1257-73. [PMID: 17409382 DOI: 10.1074/mcp.m600476-mcp200] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adipocytes are central players in energy metabolism and the obesity epidemic, yet their protein composition remains largely unexplored. We investigated the adipocyte proteome by combining high accuracy, high sensitivity protein identification technology with subcellular fractionation of nuclei, mitochondria, membrane, and cytosol of 3T3-L1 adipocytes. We identified 3,287 proteins while essentially eliminating false positives, making this one of the largest high confidence proteomes reported to date. Comprehensive bioinformatics analysis revealed that the adipocyte proteome, despite its specialized role, is very complex. Comparison with microarray data showed that the mRNA abundance of detected versus non-detected proteins differed by less than 2-fold and that proteomics covered as large a proportion of the insulin signaling pathway. We used the Endeavour gene prioritization algorithm to associate a number of factors with vesicle transport in response to insulin stimulation, a key function of adipocytes. Our data and analysis can serve as a model for cellular proteomics. The adipocyte proteome is available as supplemental material and from the Max-Planck Unified Proteome database.
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Affiliation(s)
- Jun Adachi
- Department of Proteomics and Signal Transduction, Max Planck Institute for Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
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13
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Foster LJ, Rudich A, Talior I, Patel N, Huang X, Furtado LM, Bilan PJ, Mann M, Klip A. Insulin-dependent interactions of proteins with GLUT4 revealed through stable isotope labeling by amino acids in cell culture (SILAC). J Proteome Res 2006; 5:64-75. [PMID: 16396496 DOI: 10.1021/pr0502626] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The insulin-regulated glucose transporter (GLUT4) translocates to the plasma membrane in response to insulin in order to facilitate the postprandial uptake of glucose into fat and muscle cells. While early insulin receptor signaling steps leading to this translocation are well defined, the integration of signaling and regulation of GLUT4 traffic remains elusive. Several lines of evidence suggest an important role for the actin cytoskeleton and for protein-protein interactions in regulating GLUT4 localization by insulin. Here, we applied stable isotope labeling by amino acids in cell culture (SILAC) to identify proteins that interact with GLUT4 in an insulin-regulated manner. Myc-tagged GLUT4 (GLUT4myc) stably expressed in L6 myotubes was immunoprecipitated via the myc epitope from total membranes isolated from basal and insulin-stimulated cells grown in medium containing normal isotopic abundance leucine or deuterated leucine, respectively. Proteins coprecipitating with GLUT4myc were analyzed by liquid chromatography/ tandem mass spectrometry. Of 603 proteins quantified, 36 displayed an insulin-dependent change of their interaction with GLUT4myc of more than 1.5-fold in either direction. Several cytoskeleton-related proteins were elevated in immunoprecipates from insulin-treated cells, whereas components of the ubiquitin-proteasome degradation system were generally reduced. Proteins participating in vesicle traffic also displayed insulin-regulated association. Of cytoskeleton-related proteins, alpha-actinin-4 recovery in GLUT4 immunoprecipitates rose in response to insulin 2.1 +/- 0.5-fold by SILAC and 2.9 +/- 0.8-fold by immunoblotting. Insulin caused GLUT4 and alpha-actinin-4 co-localization as revealed by confocal immunofluorescence microscopy. We conclude that insulin elicits changes in interactions between diverse proteins and GLUT4, and that cytoskeletal proteins, notably alpha-actinin-4, associate with the transporter, potentially to facilitate its routing to the plasma membrane.
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Affiliation(s)
- Leonard J Foster
- Center for Experimental BioInformatics (CEBI), Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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Padival AK, Hawkins KS, Huang C. High glucose-induced membrane translocation of PKC betaI is associated with Arf6 in glomerular mesangial cells. Mol Cell Biochem 2004; 258:129-35. [PMID: 15030177 DOI: 10.1023/b:mcbi.0000012847.86529.07] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Protein kinase C (PKC)-induced changes in glomerular mesangial cell (MC) phenotypic behavior has been implicated in diabetes. The activity of diacylglycerol-sensitive PKC isoforms in MCs is altered by ambient changes in glucose, but the regulation of PKC activity and subsequent intracellular signaling events are not yet clearly defined. Small GTP-binding proteins of the ADP-ribosylation factor (Arfs) family, may regulate protein kinase membrane recruitment and hence its activity in signaling events of non-polarized cells. Members of the ARF family may coordinate membrane dynamics and other cellular functions through their interaction with PKC. We studied the activation of Arf, PKC betaI and phospholipase D (PLD) in MCs cultured under normal or high glucose conditions. MCs cultured in high glucose medium exhibited predominantly cytosolic localization of PKC betaI, Arf3 and Arf6. However, phorbol ester (PMA) stimulation of cells cultured in high glucose significantly enhanced membrane association of PKC betaI and Arf6, but not Arf3. Using [3H]choline chloride to prelabel MCs and measuring [3H]choline-containing metabolite release as PLD activity, PMA stimulated a significant increase of PLD activity under high glucose condition. Our data suggest that Arf6 plays a specific role in activation of PKC betaI and PLD under high glucose condition, and may be a significant intracellular event in the change of the mesangial cell phenotype associated with diabetic nephropathy.
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Affiliation(s)
- Anoop Kumar Padival
- Department of Medicine, Case Western Reserve University, Cleveland, OH, USA.
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15
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Memon AR. The role of ADP-ribosylation factor and SAR1 in vesicular trafficking in plants. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1664:9-30. [PMID: 15238254 DOI: 10.1016/j.bbamem.2004.04.005] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2003] [Revised: 03/22/2004] [Accepted: 04/19/2004] [Indexed: 12/27/2022]
Abstract
Ras-like small GTP binding proteins regulate a wide variety of intracellular signalling and vesicular trafficking pathways in eukaryotic cells including plant cells. They share a common structure that operates as a molecular switch by cycling between active GTP-bound and inactive GDP-bound conformational states. The active GTP-bound state is regulated by guanine nucleotide exchange factors (GEF), which promote the exchange of GDP for GTP. The inactive GDP-bound state is promoted by GTPase-activating proteins (GAPs) which accelerate GTP hydrolysis by orders of magnitude. Two types of small GTP-binding proteins, ADP-ribosylation factor (Arf) and secretion-associated and Ras-related (Sar), are major regulators of vesicle biogenesis in intracellular traffic and are founding members of a growing family that also includes Arf-related proteins (Arp) and Arf-like (Arl) proteins. The most widely involved small GTPase in vesicular trafficking is probably Arf1, which not only controls assembly of COPI- and AP1, AP3, and AP4/clathrin-coated vesicles but also recruits other proteins to membranes, including some that may be components of further coats. Recent molecular, structural and biochemical studies have provided a wealth of detail of the interactions between Arf and the proteins that regulate its activity as well as providing clues for the types of effector molecules which are controlled by Arf. Sar1 functions as a molecular switch to control the assembly of protein coats (COPII) that direct vesicle budding from ER. The crystallographic analysis of Sar1 reveals a number of structurally unique features that dictate its function in COPII vesicle formation. In this review, I will summarize the current knowledge of Arf and Sar regulation in vesicular trafficking in mammalian and yeast cells and will highlight recent advances in identifying the elements involved in vesicle formation in plant cells. Additionally, I will briefly discuss the similarities and dissimilarities of vesicle traffic in plant, mammalian and yeast cells.
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Affiliation(s)
- Abdul R Memon
- TUBITAK, Research Institute for Genetic Engineering and Biotechnology, P.O. Box 21, 41470 Gebze, Kocaeli, Turkey.
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16
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Watson RT, Kanzaki M, Pessin JE. Regulated membrane trafficking of the insulin-responsive glucose transporter 4 in adipocytes. Endocr Rev 2004; 25:177-204. [PMID: 15082519 DOI: 10.1210/er.2003-0011] [Citation(s) in RCA: 309] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Since the discovery of insulin roughly 80 yr ago, much has been learned about how target cells receive, interpret, and respond to this peptide hormone. For example, we now know that insulin activates the tyrosine kinase activity of its cell surface receptor, thereby triggering intracellular signaling cascades that regulate many cellular processes. With respect to glucose homeostasis, these include the function of insulin to suppress hepatic glucose production and to increase glucose uptake in muscle and adipose tissues, the latter resulting from the translocation of the glucose transporter 4 (GLUT4) to the cell surface membrane. Although simple in broad outline, elucidating the molecular intricacies of these receptor-signaling pathways and membrane-trafficking processes continues to challenge the creative ingenuity of scientists, and many questions remain unresolved, or even perhaps unasked. The identification and functional characterization of specific molecules required for both insulin signaling and GLUT4 vesicle trafficking remain key issues in our pursuit of developing specific therapeutic agents to treat and/or prevent this debilitating disease process. To this end, the combined efforts of numerous research groups employing a range of experimental approaches has led to a clearer molecular picture of how insulin regulates the membrane trafficking of GLUT4.
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Affiliation(s)
- Robert T Watson
- Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
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17
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Straube S, Parekh AB. Arf-1 (ADP-ribosylation factor-1) is involved in the activation of a mammalian Na+-selective current. Biochem J 2004; 377:539-44. [PMID: 14563210 PMCID: PMC1223883 DOI: 10.1042/bj20030824] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2003] [Revised: 10/15/2003] [Accepted: 10/17/2003] [Indexed: 11/17/2022]
Abstract
Stimulation of mammalian cells often results in an increase in the intracellular Na(+) concentration, brought about by Na(+) influx into the cell via Na(+)-permeable ion channels. In some cell types, particularly renal epithelia and mast cells, non-hydrolysable analogues of GTP, such as GTP[S] (guanosine 5'-[gamma-thio]triphosphate), activate a non-voltage-activated Na(+)-selective current. We have carried out whole-cell patch-clamp experiments to examine how GTP[S] activates the Na(+) current in a rat mast cell line. The ability of GTP[S] to activate Na(+) influx was prevented by including GTP in the pipette solution, indicating the involvement of small G-proteins. Brefeldin A and Arf-1-(2-17), inhibitors of Arf-1 (ADP-ribosylation factor-1) proteins, suppressed the activation of Na(+) entry by GTP[S]. However, non-active succinylated Arf-1-(2-17) or an N-terminal myristoylated peptide directed towards Arf-5 were ineffective. Arf proteins modulate the cytoskeleton, and disruption of the cytoskeleton with cytochalasin D or its stabilization with phalloidin impaired the development of the Na(+) current. Disaggregation of microtubules was without effect. Dialysis with cAMP or inhibition of cAMP phosphodiesterase with caffeine both decreased the extent of Na(+) entry, and this was not prevented by pre-treatment with broad-spectrum protein kinase inhibitors. Collectively, our results suggest that the mechanism of activation of a mammalian non-voltage-activated Na(+)-selective current requires an Arf small G-protein, most probably Arf-1.
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Affiliation(s)
- Sebastian Straube
- Laboratory of Cellular and Molecular Signalling, Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK
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18
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Huang CF, Liu YW, Tung L, Lin CH, Lee FJS. Role for Arf3p in development of polarity, but not endocytosis, in Saccharomyces cerevisiae. Mol Biol Cell 2003; 14:3834-47. [PMID: 12972567 PMCID: PMC196575 DOI: 10.1091/mbc.e03-01-0013] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
ADP-ribosylation factors (ARFs) are ubiquitous regulators of virtually every step of vesicular membrane traffic. Yeast Arf3p, which is most similar to mammalian ARF6, is not essential for cell viability and not required for endoplasmic reticulum-to-Golgi protein transport. Although mammalian ARF6 has been implicated in the regulation of early endocytic transport, we found that Arf3p was not required for fluid-phase, membrane internalization, or mating-type receptor-mediated endocytosis. Arf3p was partially localized to the cell periphery, but was not detected on endocytic structures. The nucleotide-binding, N-terminal region, and N-terminal myristate of Arf3p are important for its proper localization. C-Terminally green fluorescent protein-tagged Arf3, expressed from the endogenous promoter, exhibited a polarized localization to the cell periphery and buds, in a cell cycle-dependent manner. Arf3-GFP achieved its proper localization during polarity growth through an actin-independent pathway. Both haploid and homologous diploid arf3 mutants exhibit a random budding defect, and the overexpression of the GTP-bound form Arf3p(Q71L) or GDP-binding defective Arf3p(T31N) mutant interfered with budding-site selection. We conclude that the GTPase cycle of Arf3p is likely to be important for the function of Arf3p in polarizing growth of the emerging bud and/or an unidentified vesicular trafficking pathway.
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Affiliation(s)
- Chun-Fang Huang
- Institute of Molecular Medicine, School of Medicine, National Taiwan University, National Taiwan University Hospital, Taipei, Taiwan, Republic of China
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19
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Vitale N, Chasserot-Golaz S, Bailly Y, Morinaga N, Frohman MA, Bader MF. Calcium-regulated exocytosis of dense-core vesicles requires the activation of ADP-ribosylation factor (ARF)6 by ARF nucleotide binding site opener at the plasma membrane. J Cell Biol 2002; 159:79-89. [PMID: 12379803 PMCID: PMC2173505 DOI: 10.1083/jcb.200203027] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The ADP ribosylation factor (ARF) GTP binding proteins are believed to mediate cytoskeletal remodeling and vesicular trafficking along the secretory pathway. Here we show that ARF6 is specifically associated with dense-core secretory granules in neuroendocrine PC12 cells. Stimulation with a secretagogue triggers the recruitment of secretory granules to the cell periphery and the concomitant activation of ARF6 by the plasma membrane-associated guanine nucleotide exchange factor, ARF nucleotide binding site opener (ARNO). Expression of the constitutively inactive ARF6(T27N) mutant inhibits secretagogue-dependent exocytosis from PC12 cells. Using a mutant of ARF6 specifically impaired for PLD1 stimulation, we find that ARF6 is functionally linked to phospholipase D (PLD)1 in the exocytotic machinery. Finally, we show that ARNO, ARF6, and PLD1 colocalize at sites of exocytosis, and we demonstrate direct interaction between ARF6 and PLD1 in stimulated cells. Together, these results provide the first direct evidence that ARF6 plays a role in calcium-regulated exocytosis in neuroendocrine cells, and suggest that ARF6-stimulated PLD1 activation at the plasma membrane and consequent changes in membrane phospholipid composition are critical for formation of the exocytotic fusion pore.
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Affiliation(s)
- Nicolas Vitale
- Unité Propre de Recherche 2356, Centre National de la Recherche Scientifique, 67084 Strasbourg Cedex, France.
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20
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Antoshechkin I, Han M. The C. elegans evl-20 gene is a homolog of the small GTPase ARL2 and regulates cytoskeleton dynamics during cytokinesis and morphogenesis. Dev Cell 2002; 2:579-91. [PMID: 12015966 DOI: 10.1016/s1534-5807(02)00146-6] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The in vivo functions of ARF-like members of the Ras superfamily of GTPases are relatively unexplored. Here we describe the analysis of C. elegans evl-20 gene that encodes a functional homolog of human ARL2. Elimination of evl-20 function results in abnormal vulval, gonad, and male tail development and disrupts embryonic proliferation, hypodermal enclosure, and elongation. Loss of evl-20 function causes specific defects in the microtubule cytoskeleton, which is the likely molecular basis for the observed defects. EVL-20 is closely associated with both the cell cortex and astral microtubules, suggesting that it may directly interact with microtubule structures at those locations. Our data indicate that EVL-20 functions in the cytoplasm and at the plasma membrane to regulate cytoskeletal dynamics during cytokinesis and morphogenesis.
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Affiliation(s)
- Igor Antoshechkin
- Department of Molecular, Cellular, and Developmental Biology, Howard Hughes Medical Institute, University of Colorado, Boulder, CO 80309, USA
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21
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Hattori MA, Fujioka T, Kato Y, Fujihara N. Preferential expression of ADP-ribosylation factor gene in the chick embryonic gonads. Life Sci 2002; 70:2031-7. [PMID: 12148695 DOI: 10.1016/s0024-3205(01)01544-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
cDNA cloning from chick embryonic gonads subtracted from tissues of the brain, heart, liver, gizzard, mesonephros and skeletal muscle was performed to identify genes with expression unique to embryonic gonads. Several cDNA clones encoding characterized as well as many uncharacterized genes were obtained. ADP-ribosylation factor (ARF) of these identified genes was preferentially expressed in the chick embryonic ovary and testis as revealed by reverse transcription-polymerase chain reaction analysis. Expression of the ARF was evaluated through embryonic development, but no difference in the transcript (relative to glyceraldehyde-3-phosphate dehydrogenase transcript) was observed between the left and right ovaries, and between the ovary and testis. In addition, the ARF transcript was detected in the gonads on embryonic days 5 to 21. These findings indicate that the ARF is constantly, but preferentially expressed in the embryonic gonads during development.
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Affiliation(s)
- Masa-aki Hattori
- Division of Animal and Marine Resource Sciences, Graduate School of Agriculture, Kyushu University, Fukuoka, Japan.
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22
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Criss AK, Silva M, Casanova JE, McCormick BA. Regulation of Salmonella-induced neutrophil transmigration by epithelial ADP-ribosylation factor 6. J Biol Chem 2001; 276:48431-9. [PMID: 11641400 DOI: 10.1074/jbc.m106969200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Salmonella typhimurium elicits an acute inflammatory response in the host intestinal epithelium, characterized by the movement of polymorphonuclear leukocytes (PMN) across the epithelial monolayer to the intestinal lumen. It was recently shown that SipA, a protein secreted by S. typhimurium, is necessary and sufficient to drive PMN transmigration across model intestinal epithelia (Lee, C. A., Silva, M., Siber, A. M., Kelly, A. J., Galyov, E., and McCormick, B. A. (2000) Proc. Natl. Acad Sci. USA 97, 12283-12288). However, the epithelial factors responsible for this process have not been identified. Here, for the first time, we demonstrate that S. typhimurium-induced PMN transmigration across Madin-Darby canine kidney-polarized monolayers is regulated by the GTPase ARF6. Apically added S. typhimurium promoted the translocation of ARF6 and its exchange factor ARNO to the apical surface. Overexpression of a dominant-negative mutant of ARF6 inhibited Salmonella-induced PMN transmigration, which was due to a reduction in apical release of the PMN chemoattractant PEEC (pathogen-elicited epithelial chemoattractant), without affecting bacterial internalization. Furthermore, ARF6 and its effector phospholipase D (PLD) were both required for bacteria-induced translocation of protein kinase C (PKC) to membranes. These results describe a novel signal transduction pathway, in which Salmonella initiates an ARF6- and PLD-dependent lipid signaling cascade that, in turn, directs activation of PKC, release of PEEC, and subsequent transepithelial PMN movement.
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Affiliation(s)
- A K Criss
- Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA
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23
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Shin OH, Couvillon AD, Exton JH. Arfophilin is a common target of both class II and class III ADP-ribosylation factors. Biochemistry 2001; 40:10846-52. [PMID: 11535061 DOI: 10.1021/bi0107391] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Arfophilin was first identified as a target protein for GTP-ARF5. The N-terminus of ARF5 (amino acids 2-17), which is distinct from that of class I or class III ARFs, is essential for binding to the C-terminus of arfophilin (amino acids 612-756). This study using GST fusion proteins in pulldown experiments in CHO-K1 cell lysates showed that, unexpectedly, ARF6 also bound to full-length arfophilin or the C-terminus of arfophilin (amino acids 612-756) in a GTP-dependent manner. Studies with ARF1/ARF6 chimeras further showed that the amino acid sequence of residues 37-80 of ARF6, which is different from the corresponding sequences in class I and class II ARFs, was essential for binding to arfophilin. Both GTP-ARF5 and GTP-ARF6 bound to arfophilin in CHO-K1 cell lysates, while GTP-ARF1 did not bind. In contrast, all three forms of ARF bound to arfaptin 2, with ARF1 showing the strongest binding. Yeast two-hybrid studies with wild-type, dominant negative, and constitutively active forms of ARF1, -5, and -6 and with ARF1/ARF6 chimeras confirmed these results, except that constitutively active ARF6 was autoactivating. Our findings suggest that both class II and III ARFs may influence the same cellular pathways through arfophilin as a common downstream effector.
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Affiliation(s)
- O H Shin
- Howard Hughes Medical Institute and Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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24
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Kristiansen S, Nielsen JN, Bourgoin S, Klip A, Franco M, Richter EA. GLUT-4 translocation in skeletal muscle studied with a cell-free assay: involvement of phospholipase D. Am J Physiol Endocrinol Metab 2001; 281:E608-18. [PMID: 11500317 DOI: 10.1152/ajpendo.2001.281.3.e608] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
GLUT-4-containing membranes immunoprecipitated from insulin-stimulated rat skeletal muscle produce the phospholipase D (PLD) product phosphatidic acid. In vitro stimulation of PLD in crude membrane with ammonium sulfate (5 mM) resulted in transfer of GLUT-4 (3.0-fold vs. control) as well as transferrin receptor proteins from large to small membrane structures. The in vitro GLUT-4 transfer could be blocked by neomycin (a PLD inhibitor), and neomycin also reduced insulin-stimulated glucose transport in intact incubated soleus muscles. Furthermore, protein kinase B(beta) (PKB(beta)) was found to associate with the GLUT-4 protein and was transferred to small vesicles in response to ammonium sulfate in vitro. Finally, addition of cytosolic proteins, prepared from basal skeletal muscle, and GTP nucleotides to an enriched GLUT-4 membrane fraction resulted in in vitro transfer of GLUT-4 to small membranes (6.8-fold vs. unstimulated control). The cytosol and nucleotide-induced GLUT-4 transfer could be blocked by neomycin and N-ethylmaleimide. In conclusion, we have developed a cell-free assay that demonstrates in vitro GLUT-4 transfer. This transfer may suggest release of GLUT-4-containing vesicles from donor GLUT-4 membranes involving PLD activity and binding of PKB(beta) to GLUT-4.
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Affiliation(s)
- S Kristiansen
- Copenhagen Muscle Research Center, Department of Human Physiology, University of Copenhagen, 13 Universitetsparken, DK-2100 Copenhagen, Denmark
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25
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Lawrence JT, Birnbaum MJ. ADP-ribosylation factor 6 delineates separate pathways used by endothelin 1 and insulin for stimulating glucose uptake in 3T3-L1 adipocytes. Mol Cell Biol 2001; 21:5276-85. [PMID: 11438681 PMCID: PMC87251 DOI: 10.1128/mcb.21.15.5276-5285.2001] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In 3T3-L1 adipocytes, both insulin and endothelin 1 stimulate glucose transport via translocation of the GLUT4 glucose carrier from an intracellular compartment to the cell surface. Yet it remains uncertain as to whether both hormones utilize identical pathways and to what extent each depends on the heterotrimeric G protein Galphaq as an intermediary signaling molecule. In this study, we used a novel inducible system to rapidly and synchronously activate expression of a dominant inhibitory form of ADP-ribosylation factor 6, ARF6(T27N), in 3T3-L1 adipocytes and assessed its effects on insulin- and endothelin-stimulated hexose uptake. Expression of ARF6(T27N) in 3T3-L1 adipocytes was without effect on the ability of insulin to stimulate either 2-deoxyglucose uptake or the translocation of GLUT4 or GLUT1 to the plasma membrane. However, the same ARF6 inhibitory mutant blocked the stimulation of hexose uptake and GLUT4 translocation in response to either endothelin 1 or an activated form of Galphaq, Galphaq(Q209L). These results suggest that endothelin stimulates glucose transport through a pathway that is distinct from that utilized by insulin but is likely to depend on both a heterotrimeric G protein from the Gq family and the small G protein ARF6. These data are consistent with the interpretation that endothelin and insulin stimulate functionally different pools of glucose transporters to be redistributed to the plasma membrane.
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Affiliation(s)
- J T Lawrence
- Department of Medicine, Howard Hughes Medical Institute, The Cox Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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26
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Cormont M, Le Marchand-Brustel Y. The role of small G-proteins in the regulation of glucose transport (review). Mol Membr Biol 2001; 18:213-20. [PMID: 11681788 DOI: 10.1080/09687680110077541] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Insulin increases the rate of glucose transport into fat and muscle cells by stimulating the translocation of intracellular Glut 4-containing vesicles to the plasma membrane. This results in a marked increase in the amount of the facilitative glucose transporter Glut 4 at the cell surface, allowing for an enhanced glucose uptake. This process requires a continuous cycling through the early endosomes, a Glut 4 specific storage compartment and the plasma membrane. The main effect of insulin is to increase the rate of Glut 4 trafficking from its specific storage compartment to the plasma membrane. The whole phenomenon involves signal transduction from the insulin receptor, vesicle trafficking (sorting and fusion processes) and actin cytoskeleton modifications, which are all supposed to require small GTPases. This review describes the potential role of the various members of the Ras, Rad, Rho, Arf and Rab families in the traffic of the Glut 4-containing vesicles.
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Affiliation(s)
- M Cormont
- INSERM E99-11 and IFR 50, Faculté de Médecine, Nice, France.
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27
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Le Stunff H, Dokhac L, Bourgoin S, Bader MF, Harbon S. Phospholipase D in rat myometrium: occurrence of a membrane-bound ARF6 (ADP-ribosylation factor 6)-regulated activity controlled by betagamma subunits of heterotrimeric G-proteins. Biochem J 2000; 352 Pt 2:491-9. [PMID: 11085943 PMCID: PMC1221481 DOI: 10.1042/0264-6021:3520491] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Both protein kinase C and protein tyrosine kinases have been shown to be involved in phospholipase D (PLD) activation in intact rat myometrium [Le Stunff, Dokhac and Harbon (2000) J. Pharmacol. Exp. Ther. 292, 629-637]. In this study we assessed the involvement of monomeric G-proteins in PLD activation in a cell-free system derived from myometrial tissue. Both the PLD1 and PLD2 isoforms were detected. Two forms of PLD activity, essentially membrane-bound, were found in myometrial preparations. One form was stimulated by oleate and insensitive to guanosine 5'-[gamma-thio] triphosphate (GTP[S]). The second required ammonium sulphate to be detected and was stimulated by GTP[S]. ADP-ribosylation factors (ARF1 and ARF6) and RhoA were immunodetected in myometrial preparations. ARF1 and RhoA were present in the membrane and cytosolic fractions whereas ARF6 was detected exclusively in the membrane fraction. A synthetic myristoylated peptide corresponding to the N-terminal domain of ARF6 [myrARF6((2-13))] totally abolished PLD activation in the presence of ammonium sulphate and GTP[S], whereas myrARF1((2-17)) and the inhibitory GDP/GTP-exchange factor, Rho GDI, did not. These data are consistent with a membrane-bound ARF6-regulated PLD activity. Finally, the stimulation of PLD by ARF6 was inhibited by AlF(-)(4) and this inhibition was counteracted by the fusion protein glutathione S-transferase-beta-adrenergic receptor kinase 1 (495-689) and by the QEHA peptide (from adenylate cyclase ACII), which act as G-protein betagamma-subunit scavengers. It is concluded that G-protein subunits betagamma are involved in a pathway modulating PLD activation by ARF6, illustrating cross-talk between heterotrimeric and monomeric G-proteins.
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Affiliation(s)
- H Le Stunff
- Signalisation et Régulations Cellulaires, CNRS UMR 8619, Bâtiment 432, Université Paris-Sud, 91405 Orsay Cedex, France
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28
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Randazzo PA, Nie Z, Miura K, Hsu VW. Molecular Aspects of the Cellular Activities of ADP-Ribosylation Factors. Sci Signal 2000. [DOI: 10.1126/scisignal.592000re1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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29
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Randazzo PA, Nie Z, Miura K, Hsu VW. Molecular aspects of the cellular activities of ADP-ribosylation factors. SCIENCE'S STKE : SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT 2000; 2000:re1. [PMID: 11752622 DOI: 10.1126/stke.2000.59.re1] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Adenosine diphosphate-ribosylation factor (Arf) proteins are members of the Arf arm of the Ras superfamily of guanosine triphosphate (GTP)-binding proteins. Arfs are named for their activity as cofactors for cholera toxin-catalyzed adenosine diphosphate-ribosylation of the heterotrimeric G protein Gs. Physiologically, Arfs regulate membrane traffic and the actin cytoskeleton. Arfs function both constitutively within the secretory pathway and as targets of signal transduction in the cell periphery. In each case, the controlled binding and hydrolysis of GTP is critical to Arf function. The activities of some guanine nucleotide exchange factors (GEFs) and guanosine triphosphatase (GTPase)-activating proteins (GAPs) are stimulated by phosphoinositides, including phosphatidylinositol 3,4,5-trisphosphate (PIP3) and phosphatidylinositol 4,5-bisphosphate (PIP2), and phosphatidic acid (PA), likely providing both a means to respond to regulatory signals and a mechanism to coordinate GTP binding and hydrolysis. Arfs affect membrane traffic in part by recruiting coat proteins, including COPI and clathrin adaptor complexes, to membranes. However, Arf function likely involves many additional biochemical activities. Arf activates phospholipase D and phosphatidylinositol 4-phosphate 5-kinase with the consequent production of PA and PIP2, respectively. In addition to mediating Arf's effects on membrane traffic and the actin cytoskeleton, PA and PIP2 are involved in the regulation of Arf. Arf also works with Rho family proteins to affect the actin cytoskeleton. Several Arf-binding proteins suspected to be effectors have been identified in two-hybrid screens. Arf-dependent biochemical activities, actin cytoskeleton changes, and membrane trafficking may be integrally related. Understanding Arf's role in complex cellular functions such as protein secretion or cell movement will involve a description of the temporal and spatial coordination of these multiple Arf-dependent events.
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Affiliation(s)
- P A Randazzo
- Laboratory of Cellular Oncology, Division of Basic Sciences, National Cancer Institute, Bethesda, MD, USA.
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Jackson TR, Brown FD, Nie Z, Miura K, Foroni L, Sun J, Hsu VW, Donaldson JG, Randazzo PA. ACAPs are arf6 GTPase-activating proteins that function in the cell periphery. J Cell Biol 2000; 151:627-38. [PMID: 11062263 PMCID: PMC2185579 DOI: 10.1083/jcb.151.3.627] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2000] [Accepted: 09/18/2000] [Indexed: 11/22/2022] Open
Abstract
The GTP-binding protein ADP-ribosylation factor 6 (Arf6) regulates endosomal membrane trafficking and the actin cytoskeleton in the cell periphery. GTPase-activating proteins (GAPs) are critical regulators of Arf function, controlling the return of Arf to the inactive GDP-bound state. Here, we report the identification and characterization of two Arf6 GAPs, ACAP1 and ACAP2. Together with two previously described Arf GAPs, ASAP1 and PAP, they can be grouped into a protein family defined by several common structural motifs including coiled coil, pleckstrin homology, Arf GAP, and three complete ankyrin-repeat domains. All contain phosphoinositide-dependent GAP activity. ACAP1 and ACAP2 are widely expressed and occur together in the various cultured cell lines we examined. Similar to ASAP1, ACAP1 and ACAP2 were recruited to and, when overexpressed, inhibited the formation of platelet-derived growth factor (PDGF)-induced dorsal membrane ruffles in NIH 3T3 fibroblasts. However, in contrast with ASAP1, ACAP1 and ACAP2 functioned as Arf6 GAPs. In vitro, ACAP1 and ACAP2 preferred Arf6 as a substrate, rather than Arf1 and Arf5, more so than did ASAP1. In HeLa cells, overexpression of either ACAP blocked the formation of Arf6-dependent protrusions. In addition, ACAP1 and ACAP2 were recruited to peripheral, tubular membranes, where activation of Arf6 occurs to allow membrane recycling back to the plasma membrane. ASAP1 did not inhibit Arf6-dependent protrusions and was not recruited by Arf6 to tubular membranes. The additional effects of ASAP1 on PDGF-induced ruffling in fibroblasts suggest that multiple Arf GAPs function coordinately in the cell periphery.
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Affiliation(s)
- T R Jackson
- Laboratory of Cellular Oncology, Division of Basic Sciences, National Cancer Institute, Bethesda, Maryland 20892-4255, USA
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Jackson TR, Kearns BG, Theibert AB. Cytohesins and centaurins: mediators of PI 3-kinase-regulated Arf signaling. Trends Biochem Sci 2000; 25:489-95. [PMID: 11050434 DOI: 10.1016/s0968-0004(00)01644-3] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Receptor-activated phosphoinositide (PI) 3-kinases produce PtdIns(3, 4,5)P(3) and its metabolite PtdIns(3,4)P(2) that function as second messengers in membrane recruitment and activation of target proteins. The cytohesin and centaurin protein families are potential targets for PtdIns(3,4,5)P(3) that also regulate and interact with Arf GTPases. Consequently, these families are poised to transduce PI 3-kinase activation into coordinated control of Arf-dependent pathways. Proposed downstream events in PI 3-kinase-regulated Arf cascades include modulation of vesicular trafficking and the actin cytoskeleton.
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Affiliation(s)
- T R Jackson
- Dept of Haematology, Royal Free and University College Medical School, Royal Free Campus, Rowland Hill St, NW3 2PF, London, UK.
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32
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Abstract
The small G proteins of the ARF family are key regulators of membrane dynamics. Many functions of ARF proteins in cells are being revealed by studies of their regulators and effectors. Significant progress has been made over the past year, with the identification of a surprisingly large family of novel ARF GTPase-activating proteins. In addition, two new classes of effectors, the PIP kinases and a novel family of monomeric coat-like proteins have been discovered.
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Affiliation(s)
- J G Donaldson
- Laboratory of Cell Biology, NHLBI, NIH, Bethesda, 20892, USA.
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Martin S, Ramm G, Lyttle CT, Meerloo T, Stoorvogel W, James DE. Biogenesis of insulin-responsive GLUT4 vesicles is independent of brefeldin A-sensitive trafficking. Traffic 2000; 1:652-60. [PMID: 11208153 DOI: 10.1034/j.1600-0854.2000.010809.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Insulin stimulates translocation of GLUT4 from an intracellular compartment to the plasma membrane in adipocytes. As a significant amount of GLUT4 is localised to the TGN, independently of the biosynthetic pathway, one possibility is that trafficking via the TGN is important in either intracellular sequestration or insulin-dependent movement to the cell surface. In this study we have used immuno-electron microscopy to show that GLUT4 is localised to AP-1 vesicles in the TGN region in 3T3-L1 adipocytes. To dissect the role of this trafficking pathway we used brefeldin A (BFA) to disrupt AP-1 association with membranes. Despite a reorganisation of GLUT4 compartments following BFA treatment, the intracellular sequestration of GLUT4, and its insulin-dependent movement to the cell surface, was unaffected. BFA increased the half time of reversal of insulin-stimulated glucose transport from 17 to 30 min but did not prevent complete reversal. Furthermore, following reversal restimulation of glucose transport activity by insulin was not compromised. We conclude that under basal conditions GLUT4 cycles between the TGN and endosomes via the AP-1 pathway. However, neither this pathway, nor any other BFA-sensitive pathway, appears to play a major role in insulin-dependent recruitment of GLUT4 to the cell surface.
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Affiliation(s)
- S Martin
- Centre for Molecular and Cellular Biology and Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia.
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Al-Awar O, Radhakrishna H, Powell NN, Donaldson JG. Separation of membrane trafficking and actin remodeling functions of ARF6 with an effector domain mutant. Mol Cell Biol 2000; 20:5998-6007. [PMID: 10913182 PMCID: PMC86076 DOI: 10.1128/mcb.20.16.5998-6007.2000] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/1999] [Accepted: 05/15/2000] [Indexed: 11/20/2022] Open
Abstract
The ADP-ribosylation factor 6 (ARF6) GTPase has a dual function in cells, regulating membrane traffic and organizing cortical actin. ARF6 activation is required for recycling of the endosomal membrane back to the plasma membrane (PM) and also for ruffling at the PM induced by Rac. Additionally, ARF6 at the PM induces the formation of actin-containing protrusions. To identify sequences in ARF6 that are necessary for these distinct functions, we examined the behavior of a chimeric protein of ARF1 and ARF6. The 1-6 chimera (with the amino half of ARF1 and the carboxyl half of ARF6) localized like ARF6 in HeLa cells and moved between the endosome and PM, but it did not form protrusions, an ARF6 effector function. Two residues in the amino-terminal half of ARF6, Q37 and S38, when substituted into the 1-6 chimera allowed protrusion formation, whereas removal of these residues from ARF6 resulted in an inability to form protrusions. Interestingly, expression of 1-6 in cells selectively inhibited protrusions induced by wild-type ARF6 but had no effect on ARF6-regulated membrane movement or Rac-induced ruffling. Thus, we have uncoupled two functions of ARF6, one involved in membrane trafficking, which is necessary for Rac ruffling, and another involved in protrusion formation.
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Affiliation(s)
- O Al-Awar
- Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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Ménétrey J, Macia E, Pasqualato S, Franco M, Cherfils J. Structure of Arf6-GDP suggests a basis for guanine nucleotide exchange factors specificity. NATURE STRUCTURAL BIOLOGY 2000; 7:466-9. [PMID: 10881192 DOI: 10.1038/75863] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Arf6 is an isoform of Arf that localizes at the periphery of the cell where it has an essential role in endocytotic pathways. Its function does not overlap with that of Arf1, although the two proteins share approximately 70% sequence identity and they have switch regions, whose conformation depends on the nature of the guanine nucleotide, with almost identical sequences. The crystal structure of Arf6-GDP at 2.3 A shows that it has a conformation similar to that of Arf1-GDP, which cannot bind membranes with high affinity. Significantly, the switch regions of Arf6 deviate by 2-5 A from those of Arf1. These differences are a consequence of the shorter N-terminal linker of Arf6 and of discrete sequence changes between Arf6 and Arf1. Mutational analysis shows that one of the positions which differs between Arf1 and Arf6 affects the configuration of the nucleotide binding site and thus the nucleotide binding properties of the Arf variant. Altogether, our results provide a structural basis for understanding how Arf1 and Arf6 can be distinguished by their guanine nucleotide exchange factors and suggest a model for the nucleotide/membrane cycle of Arf6.
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Affiliation(s)
- J Ménétrey
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Gif-sur-Yvette, France
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Caumont AS, Vitale N, Gensse M, Galas MC, Casanova JE, Bader MF. Identification of a plasma membrane-associated guanine nucleotide exchange factor for ARF6 in chromaffin cells. Possible role in the regulated exocytotic pathway. J Biol Chem 2000; 275:15637-44. [PMID: 10748097 DOI: 10.1074/jbc.m908347199] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ADP-ribosylation factors (ARFs) constitute a family of structurally related proteins that forms a subset of the Ras superfamily of regulatory GTP-binding proteins. Like other GTPases, activation of ARFs is facilitated by specific guanine nucleotide exchange factors (GEFs). In chromaffin cells, ARF6 is associated with the membrane of secretory granules. Stimulation of intact cells or direct elevation of cytosolic calcium in permeabilized cells triggers the rapid translocation of ARF6 to the plasma membrane and the concomitant activation of phospholipase D (PLD) in the plasma membrane. Both calcium-evoked PLD activation and catecholamine secretion in permeabilized cells are strongly inhibited by a synthetic peptide corresponding to the N-terminal domain of ARF6, suggesting that the ARF6-dependent PLD activation near the exocytotic sites represents a key event in the exocytotic reaction in chromaffin cells. In the present study, we demonstrate the occurrence of a brefeldin A-insensitive ARF6-GEF activity in the plasma membrane and in the cytosol of chromaffin cells. Furthermore, reverse transcriptase-polymerase chain reaction and immunoreplica analysis indicate that ARNO, a member of the brefeldin A-insensitive ARF-GEF family, is expressed and predominantly localized in the cytosol and in the plasma membrane of chromaffin cells. Using permeabilized chromaffin cells, we found that the introduction of anti-ARNO antibodies into the cytosol inhibits, in a dose-dependent manner, both PLD activation and catecholamine secretion in calcium-stimulated cells. Furthermore, co-expression in PC12 cells of a catalytically inactive ARNO mutant with human growth hormone as a marker of secretory granules in transfected cells resulted in a 50% inhibition of growth hormone secretion evoked by depolarization with high K(+). The possibility that the plasma membrane-associated ARNO participates in the exocytotic pathway by activating ARF6 and downstream PLD is discussed.
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Affiliation(s)
- A S Caumont
- INSERM, U-338 Biologie de la Communication Cellulaire, 5 rue Blaise Pascal, 67084 Strasbourg Cedex, France
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Mukherjee S, Gurevich VV, Jones JC, Casanova JE, Frank SR, Maizels ET, Bader MF, Kahn RA, Palczewski K, Aktories K, Hunzicker-Dunn M. The ADP ribosylation factor nucleotide exchange factor ARNO promotes beta-arrestin release necessary for luteinizing hormone/choriogonadotropin receptor desensitization. Proc Natl Acad Sci U S A 2000; 97:5901-6. [PMID: 10811902 PMCID: PMC18531 DOI: 10.1073/pnas.100127097] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Desensitization of guanine nucleotide binding protein-coupled receptors is a ubiquitous phenomenon characterized by declining effector activity upon persistent agonist stimulation. The luteinizing hormone/choriogonadotropin receptor (LH/CGR) in ovarian follicles exhibits desensitization of effector adenylyl cyclase activity in response to the mid-cycle surge of LH. We have previously shown that uncoupling of the agonist-activated LH/CGR from the stimulatory G protein (G(s)) is dependent on GTP and attributable to binding of beta-arrestin present in adenylyl cyclase-rich follicular membrane fraction to the third intracellular (3i) loop of the receptor. Here, we report that LH/CGR-dependent desensitization is mimicked by ADP ribosylation factor nucleotide-binding site opener, a guanine nucleotide exchange factor of the small G proteins ADP ribosylation factors (Arfs) 1 and 6, and blocked by synthetic N-terminal Arf6 peptide, suggesting that the GTP-dependent step of LH/CGR desensitization is receptor-dependent Arf6 activation. Arf activation by GTP and ADP ribosylation factor nucelotide-binding site opener promotes the release of docked beta-arrestin from the membrane, making beta-arrestin available for LH/CGR; Arf6 but not Arf1 peptides block beta-arrestin release from the membrane. Thus, LH/CGR appears to activate two membrane delimited signaling cascades via two types of G proteins: heterotrimeric G(s) and small G protein Arf6. Arf6 activation releases docked beta-arrestin necessary for receptor desensitization, providing a feedback mechanism for receptor self-regulation.
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Affiliation(s)
- S Mukherjee
- Department of Cell and Molecular Biology, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, IL 60611, USA
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38
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Abstract
Endocytosis is characterized by vesicular transport along numerous pathways. Common steps in each pathway include membrane budding to form vesicles, transport to a particular destination, and ultimately docking and fusion with the target membrane. Specificity of vesicle targeting is rendered in part by associated Rab GTPases. This review summarizes current knowledge about Rab GTPase functions in the endocytic pathways and provides insight into the regulation of Rab GTPase activity and mechanisms of Rab protein function. Functional assays have identified some Rab proteins that operate on individual pathways, but Rab proteins in several pathways remain controversial or have not been identified. Control of Rab GTPase activity is exerted through multiple levels of regulation. Significant new information pertaining to Rab protein function in regulating transport has emerged. Remarkably, Rab5 GTPase links budding, cytoskeletal transport and docking/fusion activities. This paradigm will most likely be generally applicable to other Rab GTPase pathways. Together with the cross-talk between different Rab proteins and their effectors, this may provide an integrated system for the general coordination of endocytic pathways to maintain organelle homeostasis.
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Affiliation(s)
- J Somsel Rodman
- Department of Pathology, The University of New Mexico Health Sciences Center, School of Medicine, NE, Albuquerque, New Mexico 87131-5301, USA
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Elmendorf JS, Pessin JE. Insulin signaling regulating the trafficking and plasma membrane fusion of GLUT4-containing intracellular vesicles. Exp Cell Res 1999; 253:55-62. [PMID: 10579911 DOI: 10.1006/excr.1999.4675] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- J S Elmendorf
- Department of Physiology, University of Iowa, Iowa City, Iowa, 52242-1109, USA
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